1. Field of the Invention
This invention relates to a mold and method for making a metal casting having variable hardness properties throughout the casting and, more particularly, to a mold having thermally conductive members selectively received therein wherein the conductive members create differing cooling conditions for the molded article and are easily inserted and removed from the mold. In another aspect, the invention relates to a method for making a molded article wherein the hardness of the molded article differs throughout the product.
2. Description of the Related Art
In industrial molding processes, it is known to cast metal parts in a sand or resin mold and selectively develop different metallurgical properties throughout portions of the molded article through the use of chill inserts provided in the sand or resin mold. In this process, a conventional mold is prepared and a recess is formed therein for the receipt of a small metal insert positioned in the mold such that it will contact the molten metal entering the mold cavity. As the molten metal is received in the mold cavity, the chill insert cools the molded article more quickly than the remainder of the molded article and hardens the area of the molded article immediately adjacent to the chill. The molded article and chill are removed from the mold by a "shakeout" process which requires breaking apart the mold. The chill inserts are recovered by hand sifting through the waste sand of the used mold. After the chills are recovered, they must be inspected for damage and then sorted according to size and application.
This process for molding a selectively hardened molded article is extremely labor intensive and inefficient with respect to the recovery and reuse of the chill inserts.
Other known mold assemblies for selectively hardening a molded article are seen in U.S. Pat. No. 5,072,773 issued Dec. 17, 1991 to Ruff, et al.; U.S. Pat. No. 843,679 issued Feb. 12, 1907 to Johns; Japanese Patent Document No. 59-184697 to Kuwabara dated Apr. 1, 1986; Japanese Patent Document No. JP-058741 to Shinden dated Dec. 5, 1981; Japanese Patent Document No. 60-151884 to Mai dated Jan. 22, 1987; Japanese Patent Document No. 62-217639 to Kanemitsu dated Mar. 8, 1989; and Japanese Patent Document No. 57-148258 to Kinoshita dated Mar. 3, 1984.
Each of the known molds and methods for creating a selectively hardened molded article are inefficient and require significant investments in either labor or capital equipment thereby dramatically increasing the cost for the molded article.